1. Field of the Invention
This invention relates to the addition of isolated lipoproteins to substantially human serum to prepare a stable serum standard or reference having good optical clarity, particularly upon reconstitution from the lyophilized state.
2. Description of the Prior Art
The use of human serum standards or references in blood chemistry analysis is well known. It is frequently advantageous as a diagnostic aid to determine the levels of certain constituents of a patient's blood. This determination is made with the aid of human serum standards. These serum standards are commonly stored as a dry powder after lyophilization to be reconstituted at the time of use. Alternatively they may be frozen and thawed. It is desirable that the lyophilized human serum, when reconstituted with aqueous media, be stable and have substantial optical clarity to minimize interference with the analytical measurement of serum constituents.
Two important blood constituents are triglyceride and cholesterol. It is therefore desirable to prepare a human serum standard or reference containing triglyceride or cholesterol and having good optical clarity for use with analytical testing procedures. The serum should also be stable and easily reconstituted after storage in the lyophilized or frozen state. Further, certain processes for preparing a human serum standard involve the elimination of much or all of the triglyceride and cholesterol. It then becomes necessary to provide for the addition back of triglyceride or cholesterol if these are to be measured.
The source of the triglyceride and cholesterol for preparation of a human serum standard is important. The resulting substantially human serum must be stable and have good optical clarity, even after lyophilization and reconstitution. In U.S. Pat. No. 3,764,556, issued to Kuchmak et al. on Oct. 9, 1973, there is disclosed a technique for obtaining a triglyceride-rich fraction from egg yolk. The egg yolk fraction, however, must be used the same day that it is prepared since a precipitate is formed upon freezing and thawing. The Kuchmak et al. patent additionally discloses a procedure for obtaining a cholesterol-rich B-protein fraction from outdated human plasma for use in bovine and horse sera. It is believed that this is a low density lipoprotein fraction. The use of this protein fraction however, entails several disadvantages. First, there are certain dangers involved in that the procedure by which the cholesterol-rich fraction is obtained will also result in collection and concentration of any hepatitis virus which may be present in the plasma. Additionally, it has been found that serum turbidity will result upon lyophilization and reconstitution of the prepared cholesterol standard.
In general, present methods for preparing human serum standards provide a serum which displays turbidity upon lyophilization and reconstitution with aqueous media. Also, a process which utilizes human blood as a source of triglyceride or cholesterol to be added in preparing a serum standard will generally be expensive. Further, processes using triglycerides or cholesterol from primates can present risks of hepatitis.